1. Field of the Invention
The present invention relates to a method of manufacturing a light emitting device and, more particularly, to a method of manufacturing a light emitting device including a light emitting element, a luminescent color conversion member, a reflective member and a mounting substrate.
2. Description of the Related Art
Patent Document 1 discloses a light emitting device where a light emitting element and a light transmitting member containing phosphors are bonded by a light guide member made of adhesive and the side surfaces of the light emitting element and the light transmitting member are covered by a coating material containing a light reflective material.
Further, Patent Document 1 also discloses a light emitting device where a plurality of light emitting elements that is spaced apart from each other is bonded to a light-receiving surface side of one light transmitting member through a light guide member.
Patent Document 2 discloses a light emitting device where a light emitting element is bonded to a wavelength conversion member containing phosphors. Here, the light emitting element has a first region and a second region from the wavelength conversion member side. The wavelength conversion member has a third region and a fourth region from the light emitting element side. The first region has an irregular atomic arrangement, as compared to the second region. The third region has an irregular atomic arrangement, as compared to the fourth region. The first region is directly bonded to the third region.
Further, Patent Document 2 discloses a surface activated bonding method where the bonding surfaces of the light emitting element and the wavelength conversion member are sputter-etched by an ion beam or plasma or the like, both bonding surfaces are activated, and then the light emitting element and the wavelength conversion member are directly bonded at the bonding surfaces.
Meanwhile, it is difficult to bond the light emitting element including a sapphire substrate and the wavelength conversion member made of a glass by the surface activated bonding method. Accordingly, in Patent Document 2, aluminum oxide is formed as a bonding member on the glass surface by a sputtering or the like and the aluminum oxide and the sapphire substrate are bonded by the surface activated bonding method.
Patent Document 1: JP-B-5326705
Patent Document 2: WO2011/126000
In a light emitting device including a light emitting element and a luminescent color conversion member (wavelength conversion member) containing phosphors, a primary light (blue light) is an excitation light emitted from the light emitting element and a portion of the primary light is excited by the phosphors in the luminescent color conversion member to generate a luminescent color-converted (wavelength-converted) secondary light (yellow light). The primary light and the secondary light are mixed to generate a mixed-color light (white light). The mixed-color light is emitted to the outside from the light emitting device through the luminescent color conversion member.
Therefore, light energy that is not converted during the luminescent color conversion becomes thermal energy to cause the phosphors to generate heat. Accordingly, the temperature of the phosphors is raised and the efficiency of the luminescent color conversion is lowered. Further, the components of the light emitting device are deteriorated due to the heat-generation. Accordingly, it is necessary to efficiently dissipate the heat generated by the phosphors.
However, in the technique disclosed in Patent Document 1, the light emitting element and the light transmitting member (luminescent color conversion member) are bonded by the light guide member. Further, the light guide member made of an adhesive has a low thermal conductivity. Accordingly, the heat transfer to the light emitting element from the light transmitting member is blocked by the light guide member.
As a result, there are problems that the temperature of phosphors contained in the light transmitting member is raised, the efficiency of luminescent color conversion is lowered, and the components of the light emitting device are deteriorated due to the heat-generation.
Further, in the technique disclosed in Patent Document 1, the light transmitting member is mounted by being placed on the upper surface of the light emitting element through the light guide member. However, from the viewpoint of the mounting accuracy, it is difficult to cause the size of the light emitting element to be equal to that of the light transmitting member, as seen in a plan view. Further, it is necessary to cause the size of the light transmitting member to be greater than that of the light emitting element, as seen in a plan view.
Therefore, a cover portion covering the upper surface of the light emitting element and an eaves-like portion extending from the cover portion are formed in the light transmitting member.
As a result, in addition to the light emitted through the light transmitting member from the upper surface of the light emitting element, the light emitted through the eaves-like portion of the light transmitting member from the side surface of the light emitting element also occurs.
Then, the light emitted through the light transmitting member from the upper surface of the light emitting element is a white light whereas the light emitted through the eaves-like portion of the light transmitting member from the side surface of the light emitting element is a yellow light. Accordingly, there is a possibility that the in-plane distribution of chromaticity in the front surface of the light transmitting member becomes uneven.
Further, in the technique disclosed in Patent Document 1, one light transmitting member also covers gaps between the pluralities of light emitting elements.
Therefore, the light emitted through the light transmitting member from the upper surface of each light emitting element is a white light whereas the light emitted through the gaps and then through the light transmitting member from the side surface of each light emitting element is a yellow light. Accordingly, there is a possibility that the in-plane distribution of chromaticity in the front surface of the light transmitting member becomes uneven.
Further, when there is a variation in the thickness (height) of each light emitting element, for each light emitting element, a variation occurs in distances between the upper surface of each light emitting element and one light transmitting member. Accordingly, a temperature distribution occurs in the light transmitting member and cracks due to thermal stress are generated in the light transmitting member. Accordingly, there is a possibility that the light transmitting member is broken.
In the technique disclosed in Patent Document 2, the atomic arrangement in the bonding surface between the light emitting element and the wavelength conversion member is irregular. Accordingly, a compositional change occurs in the surface state of the bonding surface. As a result, optical characteristics also change in accordance with the compositional change.
Therefore, the emitted light of the light emitting element is unnecessarily reflected or absorbed by the bonding surface and it is thus difficult to cause the emitted light of the light emitting element to be smoothly incident on the wavelength conversion member. Accordingly, there is a problem that the light extraction efficiency is lowered.
Further, in the technique disclosed in Patent Document 2, the emitted light of the light emitting element is reflected or absorbed by a bonding member when the bonding member is formed between the light emitting element and the wavelength conversion member. Accordingly, it is difficult to cause the emitted light of the light emitting element to be smoothly incident on the wavelength conversion member.